Remember Tabby’s Star? It’s the star that astronomer Tabetha Boyajian – who reported its strangeness in a Ted Talk in February, 2016 – famously called “the most mysterious star in the galaxy.” It’s mysterious because astronomers have never seen another star do what this star does. One explanation for the strange dimming of its light is that the star has an alien-built megastructure – a Dyson sphere – around it. Does it? Will we ever know for sure? Those are unanswered questions, but, while you’re pondering it, here’s the latest on this wonderful star.

On August 3, 2016, two astronomers added more evidence that Tabby’s Star – also known as KIC 8462852 – is just plain strange. Benjamin Montet with the California Institute of Technology and Joshua Simon with Observatories of the Carnegie Institution of Washington have uploaded their paper to the arXiv preprint server detailing their study of the star by analyzing data from the NASA’s Kepler space telescope (a famed planet-finding telescope) over the past four years.

They found that the star has been decreasing in brightness at an unprecedented rate.

Finder chart for KIC 8462852. It’s located in the direction to the constellation Cygnus, which is part of the famous Summer Triangle asterism, visible at this time of year.

Now here’s some history. It’s the job of the Kepler spacecraft to look for tiny dips in a star’s light, caused by possible planets passing in front of the star. Professional astronomers analyzing data from Kepler, and citizen scientists from the Planet Hunters crowdsourcing program, noticed the star KIC 8462852 from among the 150,000 stars examined by Kepler. They noted that it is “strange” and “bizarre.” Tabitha Boyajian first reported anomalies in the unusual light curve of star KIC 8462852—over the years 2009 to 2013. Its light appeared to dip in ways that did not conform to what would be expected if it were due to a planet passing in front of it, temporarily blocking some of its light.

Her paper led to observations, commentaries and theories from others in the space community. In June, astronomers raised more than $100,000 from a Kickstarter campaign to be able to study the star further.

But no one has been able to come up with a reasonable explanation for Tabby’s Star. One idea is that comet swarms surround the star. Another is similar, but it’s planetary remnants, not comets. Then there’s the exceedingly satisfying and exciting idea that the dips in the star’s light might be due to an alien megastructure being built around the star. So far, none of the theories has been able to take into account all of the odd observations.

Earlier this year, Bradley Schaefer with Louisiana State University published results of his efforts studying photographic plates that had captured the star going back to the 19th century (see EarthSky’s article about Schaefer’s research here). He reported that a long-term dimming in the light from the star by nearly 20 percent over just the past century. That result might suggest a megastructure in the process of being built, hiding more and more of the star’s light from our view. His report was not received warmly by all, but Schaefer answered back that the criticisms were unfounded.

And now, using a different approach, Montet and Simon have found something similar to what Schaefer found. They studied images from Kepler and found that light from Tabby’s Star had decreased in brightness by approximately .34 percent a year for 1,000 days starting in 2009, which was actually twice the rate that Schaefer had found.

Even stranger, they found that over the next 200 days, the brightness of the star dimmed by another 2.5 percent before it finally leveled out.

Why don’t astronomers just turn their telescopes on this star, and figure it out? Because telescope time is expensive. Hence Boyajian’s recent and thankfully successful Kickstarter campaign.

So the mystery continues. Along with many in the astronomical community, we’ll be watching for more news!

Bottom line: Tabby’s Star – aka KIC 8462852 – behaves like no other star in the universe. Astronomers are struggling to explain it. Some think it might be a sign of an alien megastructure, or Dyson sphere, in the making. Here’s the latest.

Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.